The present patent application relates to an improver for fully or partially baked products reheated by microwave irradiation.
The request for food products which can be thawed and/or heated in microwave ovens is continually increasing, as well as the consumption of these products.
Families, catering companies, restaurants and fast food chains confirm this tendency. The consumer wants a high quality product, comparable to the standard food product, providing a minimal preparation time.
Several sources describe how baked products which have been exposed to microwave irradiation, have an increased toughness and a rubber or leatherlike texture. Immediately after reheating with microwave irradiation, the baked products are extremely soft, but during the process of cooling down, toughness increases quickly; and after a while, hardening too. Limiting or preventing the humidity loss, does not solve the problem.
At least four published hypotheses try to explain the cause of increased toughness:
(1) During the conventional baking process, amylose leaks out of the starch granules. These amylose molecules, leaked out of the starch granule, surround the granule, and orient themselves in the same direction. They are partially responsible for the bread crumb's quick hardening. Gradual retrogradation of amylopectin explains the ageing process over a longer period. (Stoch, T. J., Starch in Bakery Products, Bakers Digest 39 (2), 48-57 (1965)). When exposed to microwave irradiation, more amylose leaks out of the starch granule. This amylose is less oriented and contains less bound water than a conventionally reheated bread.
A possible cause could be the more intense agitation of amylose molecules in the microwave oven. (Mudgett, R. E., Wang, D. I. C., and Goldblith, S. A. 39, 632-635.: Prediction of Dielectric Properties in Oil-water and Alcohol-water Mixtures at 3000 Mhz, 25.degree. C. Based upon Pure Component Properties, Journal of Food Science (1974)).
Such a degree of disorder between amylose chains and perhaps also between gluten polymers determines the extremely high initial degree of softness.
During conventional reheating, less amylose leaks out of the starch granules, and there is also less disorder between the amylose chains. This results in an initially harder bread crumb.
During cooling and storage, the opposite situation takes place.
After having been exposed to microwave irradiation, the amylose, leaked out of the starch granules, has more ability to form crystalline structures, than if it were reheated in a conventional way. (Higo, A., Shimzaki, M., Noguchi, S. and Nazakawa, F., part 9, 34, 251-257: Hardening of Food Texture Induced by Microwave Irradiation, Japanese Journal of Home Economics (1983)).
Baked products age (=amongst others hardening of the crumb) quickly after microwave irradiation, because the amylose chains orient themselves in rigid structures.
(2) A second hypothesis relies upon the "Pseudo- Hydration Effect", as described by Higo and Noguchi. (Higo, A. and Noguchi, S., 34(12), 781-787: Comparative Studies on Food Treated with Microwave and Conductive Heating, Process of Bread Hardening by Microwave Heating, Journal of Japanese Society of Food Science and Technology. (1987)).
When the bread is reheated with microwave irradiation, the system behaves as if more water were present. Heating of the starch granules in an excess of water gives a similar effect:
increased leaking of amylose out of the starch granules; PA1 the initial disorder between the amylose chains increases, because there is a better dispersion in the excess of water; PA1 upon cooling and storage, the retrogradation in the amylose fraction is increased, because polymers have an enhanced tendency to orient themselves into tight crystalline bundles of double amylose helixes. PA1 milk proteins, PA1 fat, PA1 egg powder, PA1 lecithin, and PA1 microcrystalline cellulose. PA1 fat, PA1 proteins selected from the group consisting of soy and egg proteins, PA1 methylcellulose (E461). PA1 5-15 weight % proteins selected from the group consisting of soy and egg proteins, PA1 40-60 weight % fat PA1 1-6 weight % methylcellulose. PA1 0.5-3% on flour weight proteins selected from the group consisting of soy and egg proteins, PA1 4-15% on flour weight fat and PA1 0.1-1.2% on flour weight methylcellulose and (the weight percentages are based on the total flour weight).
When microwave reheating, the water in the bread crumb behaves as if it were less bound, compared to conventional heating.
The system behaves as if more water or water with an enhanced mobility were present.
(3) Molecular agitation of dipoles through microwave irradiation causes heat and can have such a strong effect on the starch granules that the macromolecular structure of the starch is (temporarily) lost.
Immediately after microwave treatment , the bread becomes extremely soft, almost fluid, as a consequence of the temporary or maybe partial liquefaction of the starch (Higo et al., part 10, 34, 474-479: Hardening of Food Texture Induced by Microwave Irradiation, Japanese Journal of Home Economics (1983)).
(4) Reheating of food products with microwave irradiation causes a strong increase in toughness.
Toughness is an elastic property (Huang, V.T. et al., Starch-Based Products for Microwave Cooking or Heating, U.S. Pat. No. 5035904 (1991)).
The enhanced softness and the lack of elasticity in bread, immediately after heating in the microwave oven, disappears upon cooling, and becomes a tough, rubberlike and hard texture which does not occur in conventional heating.
Rogers et al. (Rogers, D. E., Doescher, L. C. and Hoseney, R. C., 67 (2), 188-191: Texture Characteristics of Reheated Bread, Cereal Chemistry (1990)) noticed that increased cross-linking between protein polymers is more than likely not the cause of the product's toughness.
Hydrogen bonds (at temperatures around 100.degree. C.) cannot exist and account for toughness.
A possible explanation for increased toughness is based on the hypothesis that microwave heating orients gluten polymers in such a way that, during cooling, unusually strong hydrogen bonds may create rubberiness.
Polymer orientation can also result into increased hydrophobic interactions (Martin, M. L., Zeleznak, K. J. and Hoseney, R. C., 68(5), 498-503: A Mechanism of Breadfirming, Role of Starch Swelling, Cereal Chemistry (1991)).
EP-0620975 A2 describes a method to thaw and heat low fat baked products, with microwave irradiation. In this patent application, steam is the only heat source used to bake the fermented piece of dough. After freezing, the baked products are thawed and reheated with microwave irradiation. This operating mode only has a limited area of application.
The U.S. Pat. No. 5,110,614, describes an operating mode to prepare baked products, used for reheating in a microwave oven, and based upon a premix or a complete mix. This patent analyses the problem of the baked products' toughness, in microwave applications, and proposes the usage of a premix in powder form, or a complete mix, composed as following:
Although there is an improvement compared to an end product without this additive, it has been noted that the use of such a product in baked products, does not yield a satisfying result, because the baked end product remains tough and rubberlike after having been exposed to microwave irradiation. The results are even less conclusive when thawing and heating the frozen product.
The document Cereal Foods World, November 1991, volume 36 number 11 pages 941-944 (XP 000617106, Bell and Steinke), describes an evaluation of the effects on structure and texture of methylcellulose gums in microwave-baked cakes. An improvement in cake volume, structure and moisture retention is observed when baking cakes with microwave irradiation. This improvement is assayed using hydroxypropyl methylcellulose. It has to be stressed that this product has no significant effect on toughness in yeast-raised baked products. Toughness was not assayed, and only one type of baked good was tested. Cake is chemically leavened with a high sugar content of more than 15%.
In WO 93/16598, cellulose ethers are used to partly replace flour or starch in low-cholesterol cookies. The dough contains 50% or less flour or starch. The function of the cellulose ethers is to improve palatability.